Abstract
In the present study, 2198 Al-Cu-Li alloys were successfully friction stir welded by using various welding speed ranges of 90~180 mm/min with an invariable rotation speed of 950 r/min. The effect of welding speed on microstructure evolution and mechanical properties of the joints was investigated. The results show that, with the welding speed decreasing, the size of the nugget zone (NZ) first increases and then decreases due to different welding temperatures. At a welding speed of 150 mm/min, the size of the NZ in all joints is the biggest and the “S” curve disappears. The equiaxed grains are finer, attributed to a higher degree of dynamic recrystallization, and a larger number of fine reprecipitated phase (δ’, β’ phases) particles are dispersively distributed in the NZ. Correspondingly, the joints have the highest tensile properties, and the tensile strength, yield strength and elongation are, respectively, 406 MPa, 289 MPa and 7.2%. However, compared to the base material, the tensile properties of all joints are reduced because a greater amount of δ’ and β’ phases particles are dissolved in the NZ. Only the joints produced at 150 mm/min are fractured in the TMAZ with detected deep dimples and tearing ridges, and a significant necking phenomenon is observed, which indicates a complete ductile fracture mode.
Highlights
Compared with traditional aluminum (Al) alloys, the third generation aluminum– lithium (Al–Li) alloy is the most desirable metal material, which is attributing to lower density [1], higher mechanical properties [2], better corrosion resistance [3] as well as better super plasticity [4]
The 2198 Al-Cu-Li alloys have been successfully joined by friction stir welding at different welding speeds with an invariable rotation speed
The main conclusions are as follows: 1. With the welding speed decreasing from 180 mm/min to 90 mm/min, the size of the nugget zone (NZ) first increases and decreases due to different welding temperatures
Summary
Compared with traditional aluminum (Al) alloys, the third generation aluminum– lithium (Al–Li) alloy is the most desirable metal material, which is attributing to lower density [1], higher mechanical properties [2], better corrosion resistance [3] as well as better super plasticity [4]. Li is a very light metal and the solubility of the Li element in the Al alloy is very high [5] Due to this feature, when 1% Li element is added into Al alloy, the density of the Al–Li alloy will be reduced by about 3% [6], and its elastic modulus will be increased by nearly 6% [7]. This generation of Al–Li alloy is thought to be one of the most ideal metal materials for aerospace applications [8]. As one of the solid-state welding technologies, friction stir welding (FSW), in which the base material does not melt in the welding process [12] and the welding heat input is low, can avoid the above-mentioned metallurgical defects during the fusion welding process [13], and is deemed to be the most ideal welding method for Al–Li alloy
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